Pass -std=gnu++0x in build_nexe.py.
Pass -std=gnu++0x in build_nexe.py.

Doing this here instead of untrusted.gypi since the option isn't valid for
C files.

BUG=chromium:414314
CQ_EXTRA_TRYBOTS=tryserver.chromium.linux:linux_rel_precise32,linux_nacl_sdk,linux_chromium_dbg,linux_arm_cross_compile
R=dschuff@chromium.org

Review URL: https://codereview.chromium.org/571143002

git-svn-id: 721b910a23eff8a86f00c8fd261a7587cddf18f8@13748 fcba33aa-ac0c-11dd-b9e7-8d5594d729c2

sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client,sbc100/native_client